Propeller pod

ABSTRACT

The invention relates to a propeller pod ( 14 ) having a body ( 16 ) which has a shaft ( 18 ) for attachment to a vehicle ( 10 ), in particular to a watercraft, wherein the shaft ( 18 ) extends along a shaft axis (A S ) and has at least one cross section (Q) with a chord (S), and (b) at least one propeller shaft ( 20, 24 ) for attachment of a propeller ( 22 ), (c) wherein the chord (S) runs at a direction angle (α) with respect to a propeller rotation axis (A P ) of the propeller shaft ( 20, 24 ). The invention provides that the direction angle (α) changes, at least in places, with the distance (r) from the propeller rotation axis (A P ).

This non-provisional patent application claims priority to and the benefit of German Patent Application (DE) 10 2009 033 554.4, filed Jul. 16, 2009.

BACKGROUND AND SUMMARY OF THE DISCLOSURE

The invention relates to a propeller pod having (a) a body which has a shaft for attachment to a vehicle, in particular to a watercraft, wherein the shaft extends along a shaft axis and has at least one cross section with a chord, and (b) at least one propeller shaft for attachment of a propeller, wherein the chord runs at a direction angle with respect to a propeller rotation axis of the propeller shaft with respect to a direction angle measurement surface.

Propeller pods such as these are used in so-called pod propulsion systems. Pod propulsion systems are used when, for example in the case of marine vessels, a particularly high efficiency and compact design are desired. Pod propulsion systems are therefore used, for example, in ferries and on yachts.

EP 1 336 561 B1 discloses a pod propulsion system. This embodiment has the disadvantage that the efficiency is unsatisfactory. At high speeds, pod propulsion systems such as these tend to cavitate.

A further propeller pod is disclosed in DE 35 19 103. In this embodiment, the shaft is prismatic and is at a fixed direction angle relative to the rotation axis of the propeller. Even pod propulsion systems such as these have a tendency to cavitate. The shaft is made long and thin, and is attached to the marine-vessel hull such that it can rotate, in order to reduce cavitation.

The invention is based on the object of overcoming the disadvantages in the prior art.

The invention solves the problem by a propeller pod of this generic type in which the direction angle changes, at least in places, with the distance from the propeller rotation axis.

This propeller pod has the advantage that it is more efficient. This is because the change in the direction angle as a function of the height results in the spinning movement, which is introduced into the water flow by the traction propeller, passing over the shaft with particularly little drag.

Because of the high efficiency, a pod propulsion system having the propeller pod according to the invention is furthermore not very likely to cavitate.

A further advantage is that the abovementioned advantages can be achieved with relatively simple design measures.

For the purposes of the present description, the body means in particular all those components of the propeller pod which are externally visible and do not rotate during operation.

The shaft of the body means in particular a part of the propeller pod by means of which the propeller pod is attached to a vehicle, in particular to a watercraft. When installed, the shaft axis generally runs at an angle of approximately 90° to a tangential surface of the marine vessel hull. The shaft axis generally runs vertically.

The feature in which the shaft axis has at least one cross section with a chord means in particular that it is possible, but not necessary, for all the cross sections to be of the same type. For example, it is possible for the cross sections to be similar or even identical in the mathematical sense. It is therefore possible, for example, for a cross-sectional area of the shaft to vary with the distance from the traction propeller rotation axis.

The feature in which the chord runs at a direction angle with respect to the traction propeller rotation axis of the propeller means, in particular, that this direction angle is defined with respect to a reference surface. This reference surface may be a surface which is curved. By way of example, the reference surface is a cylindrical envelope surface of a cylinder whose longitudinal axis coincides with the traction propeller rotation axis.

Alternatively, it is also possible for the reference surface to be chosen as a plane which runs at right angles to the shaft axis. The reference surface is in this case always chosen such that the chord is defined uniquely. The chord is the connection between the profile nose and the profile trailing edge of the cross section. The term profile chord is therefore also used in this context. The profile nose can also be referred to as the incident-flow point, and the profile trailing edge as the separation point.

The feature in which the direction angle changes, at least in places, with the distance from the traction propeller rotation axis means, in particular, that it is possible for the direction angle to be independent of the distance from the traction propeller rotation axis in other sections. In other words the shaft may be in the form of a pyramid or prism in places.

It is also possible for a longitudinal body which is attached to the shaft and extends along the propeller rotation axis to be twisted in an area which extends in an extension of the shaft. This is because the shaft will generally merge continuously into the longitudinal pod. This means that said area has a local longitudinal axis which runs at the direction angle with respect to the propeller axis. By way of example, the direction angle is measured in this area on a plane which is horizontal in the installed position. Where the present description refers to the direction angle, this should also be understood as meaning that this angle is formed in said area of the longitudinal pod.

The invention is based on the discovery that it is advantageous for the shaft and/or at least parts of the longitudinal pod to be twisted. In contrast to the situation with wings surfaces, the aim of this twist, however, is not to prevent sudden complete flow separation by the flow separation first of all occurring close to the body. This is because the shaft generally has a shape such that, overall, the flow does not result in any forces being transmitted to the marine vessel hull in the lateral direction. In fact, the twist is used to reduce the drag.

The propeller is preferably a traction propeller which is attached to a traction propeller shaft. According to one preferred embodiment, the propeller pod has a pusher propeller shaft for rotation of a pusher propeller, wherein the shaft is arranged between the traction propeller and the pusher propeller with respect to a longitudinal axis of the body or of the propeller rotation axis. In other words, the water first of all flows to the traction propeller, which passes it over the shaft to the pusher propeller. The traction propeller and pusher propeller are preferably designed such that the water flow has essentially no spin downstream from the pusher propeller. This can be achieved by the traction propeller having a larger diameter than the pusher propeller. The pusher propeller shaft and the traction propeller shaft may be considered to be shaft elements of the propeller shaft, even if they are not connected to one another such that they rotate together. In general, they run coaxially.

The traction propeller shaft is particularly preferably designed to rotate the traction propeller in a traction propeller rotation direction, whereas the pusher propeller shaft is designed to rotate the pusher propeller in a pusher propeller rotation direction, which is opposite the traction propeller rotation direction. For this purpose, the propeller pod generally has a gearbox, preferably a bevel-gear gearbox.

A pod propulsion system having the propeller pod according to the invention is therefore a contrarotating propulsion system. Therefore, a propeller pod of this generic type, in which the traction propeller shaft and the pusher propeller shaft are designed to rotate the respective propellers in opposite rotation directions, with the shaft being arranged between the two propellers, is also according to the invention. Until now, the only pod propulsion systems which have been known are those in which contrarotating propellers are in each case arranged on the same side of the shaft. This is because, in previous propeller pods, the drag on the shaft would be disproportionately high because of the spin resulting from the flow of the traction propeller, as a result of which no propeller pods were built in which two contrarotating propellers are separated by the shaft. The high drag is greatly reduced by the optimized shaft shape. Furthermore, oscillations which otherwise occur are avoided. The preferred embodiments mentioned in the present description also relate to this invention.

According to one preferred embodiment, the shaft is designed such that the direction angle passes through a direction angle maximum as a function of the distance from the traction propeller rotation axis. It has been found that the precise profile of the direction angle is dependent, as a function of the distance, on the power which has to be transmitted from the pod propulsion system. In this case, it had been found to be particularly advantageous to choose a profile which passes through a maximum.

The distance which is associated with the direction angle maximum is particularly preferably at most 0.6 times a propeller radius. When there is only one propeller, the propeller radius means its diameter. When there are two or more propellers, the propeller radius means, in particular, the diameter of the propeller located furthest forward in the flow direction.

It is advantageous for the distance which tends to the direction angle maximum to correspond at most to half the traction propeller radius. Furthermore, it has been found to be advantageous for the distance which is associated with the direction angle maximum to be at least 0.2 times the propeller radius.

According to one preferred embodiment, the traction propeller has a downstream flow angle, at which water which is conveyed by the traction propeller flows away from the traction propeller, with respect to a longitudinal plane which runs parallel through the traction propeller rotation axis and preferably runs vertically in the operating position. The shaft is designed such that the direction angle differs by at most 10 degrees, in particular 5 degrees, from the downstream flow angle. This has the advantage that the majority of the water flowing away from the traction propeller passes tangentially over the shaft. This reduces vortex losses, and reduces the tendency to cavitate.

According to one preferred embodiment, at least in places, the cross sections of the shaft are similar in the mathematical sense in particular with respect to a cross section in a cylindrical coordinate system with the origin on the traction propeller rotation axis. In one special case, the cross sections are the same, that is to say they are similar and have the same area. This makes it possible to produce a shaft of particularly simple design, which at the same time produces only small lateral forces.

At least in places, the cross sections of the shaft are preferably mirror-image symmetrical. In this case, the characteristic of minor-image symmetry preferably once again relates to the cross section with respect to a cylindrical coordinate system with the origin on the traction propeller rotation axis.

At least in places, the cross sections of the shaft preferably have a thickness setback of more than 40% and in particular of less than 60%. Cross sections such as these particularly effectively reduce the drag. The thickness setback is measured with respect to the propeller rotation axis, from the projection of the incident-flow edge onto the propeller rotation axis.

A projection of an incident-flow edge of the shaft onto a lateral plane which is at right angles to the traction propeller rotation axis preferably has a curved profile. In other words, the cross sections are twisted relative to their neighbors, and are possibly also moved linearly. If the cross sections are only twisted, then there is a point in the cross section which does not change its position and is located in an interior of the cross section. The interior of the cross section means the region which is similar to the cross section, which has the same geometric centroid, and whose area is a quarter of the area of the cross section.

A projection of a separation edge of the shaft onto a lateral plane which is at right angles to the traction propeller rotation axis is preferably likewise curved profile.

Since the projection of the incident-flow edge and/or of the separation edge is curved, the water flow coming from the traction propeller flows past the shaft optimally as a function of the distance of the position under consideration from the traction propeller rotation axis. The drag is therefore minimized, and the efficiency rises.

Each cross section preferably has two outermost points of maximum discrepancy from the chord and a thickness setback point at which the chord is cut by a connection straight line through the outermost points, wherein the thickness setback points lie on a curve which is curved at least in places. This straight line preferably runs through the interior of the cross section.

At least in places, a drive shaft preferably runs through an interior of the cross section, wherein the interior is an imaginary surface which has one quarter of the area of the cross section, and has the same centroid.

It is advantageous for the direction angle to have a minimum adjacent to the marine vessel hull. By way of example, the shaft preferably merges into the marine vessel hull with a direction angle of essentially 0°, that is to say in particular of less than 5°. In general, the area of the shaft with the minimum direction angle is located at the junction between the shaft and the marine vessel hull.

A projection of the shaft onto the lateral plane is preferably concave or bi-concave, at least in places. In other words, this means that the cross section of the shaft first of all decreases, and then increases again, as the distance from the traction propeller rotation axis increases. This minimizes the drag which the propeller pod is subject to from the surrounding fluid, for example the water. It is advantageous for the point of minimum cross section to be at a distance from the traction propeller rotation axis which is greater than the rotor diameter.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in more detail in the following text with reference to the attached drawings, in which:

FIG. 1 shows a marine vessel according to the invention having a pod propulsion system according to the invention, which itself has a propeller pod according to the invention,

FIG. 2 shows a view in the direction A of the pod propulsion system shown in FIG. 1,

FIG. 3 has figure elements 3 a and 3 b which show a series of cross sections based on a plurality of direction angle measurement surfaces,

FIG. 4 shows a curve which indicates the direction angle as a function of the distance from the traction propeller rotation axis,

FIG. 5 shows a curve which indicates a thickness of the cross section as a function of the distance from the traction propeller rotation axis, and

FIG. 6 shows a view from above.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a marine vessel 10 with a marine vessel hull 12 to which a propeller pod 14 is attached, for example rigidly. The propeller pod 14 has a body 16 which itself has a shaft 18. The shaft 18 extends along a shaft axis A_(S) which generally runs vertically in the installed position, that is to say when the marine vessel 10 is not moving.

The propeller pod 14 furthermore has a traction propeller shaft 20, to which a traction propeller 22 is attached. A pusher propeller 26 is fitted to a pusher propeller shaft 24 of the propeller pod 14. The traction propeller 22 and the pusher propeller 26 rotate about a propeller rotation axis A_(P), from which a radial distance r is measured.

FIG. 2 shows a view corresponding to the arrows A in FIG. 1 of the traction propeller 22. Direction angle measurement surfaces F in the form of direction angle measurement surfaces F_(H1), F_(H2) are shown, which are each cylindrical envelope surfaces with respect to a cylinder whose longitudinal axis coincides with the propeller rotation axis A_(P). Unless stated to the contrary, the details quoted in the following text always refer to the cylindrical coordinate system, whose origin is the propeller rotation axis A.

FIG. 2 a shows a view in the direction A (cf. FIG. 1). This figure shows an incident-flow edge 28 of the shaft 18, which has a curved profile with respect to a lateral plane E_(Q). The lateral plane E_(Q) is that plane which is at right angles to the propeller rotation axis A_(P) and to all direction angle measurement surfaces F_(H).

FIG. 2 b shows a view in the direction B (cf. FIG. 1), in which a separation edge 29 can be seen, which likewise has a curved profile and departs from a horizontal H as the distance from the marine vessel hull increases, until it passes through a maximum, which is not shown.

FIG. 3 shows cross sections Q1, Q2 through the shaft 18 at two radial distances r. FIG. 3 b shows the case when r=R, which corresponds to the direction angle measurement surface F_(H1) (cf. FIG. 2). By way of example, FIG. 3 a corresponds to the case in which r =0.5R. As can be seen, there is a direction angle α between a chord S and the propeller rotation axis A_(P). As is shown in FIG. 3, the direction angle α is measured on the direction angle measurement surface F_(H). The chord S runs from an incident-flow point 30, at which it cuts the incident-flow fluid, to a separation point 32. The set of all the separation points forms the separation edge 29 of the shaft 18, and the incident-flow points 30 form the incident-flow edge 28 (FIG. 1).

The profiles Q shown in FIGS. 3 a and 3 b each have a thickness setback D, which is indicated as a proportion of the chord length L. In the present case, the thickness setback D is about 60%, and is measured from the incident-flow edge. The details relate to a projection onto the propeller rotation axis A_(P), as is shown in FIG. 3.

Furthermore, FIG. 3 b shows a drive shaft 34, which originates from a gearbox that is shown schematically in FIG. 1 and produces a drive torque for the two propellers 22, 28. The drive shaft 34 passes through an interior 40 of the shaft 18. The interior 40 is the imaginary surface which has the same centroid as the cross section Q, is similar to the cross section Q, and whose area is a quarter of that of the cross section Q.

The drive shaft 34 (FIG. 1) is connected to the propellers 22, 26 such that a pusher propeller rotation direction ω₂₆ of the pusher propeller 26 is opposite a traction propeller rotation direction ω₂₂ of the traction propeller 22.

Furthermore, FIG. 3 b shows that the cross section Q has two outermost points P1, P2 of maximum discrepancy from the chord S and a thickness setback point P_(D) at which the chord S is cut by a connection straight line through the outermost points P1, P2. The thickness setback points P_(D) are located, at least in places, on a curve with respect to a longitudinal extent of the shaft 18, which curve passes through the interior 40. The curve may also be a straight line.

FIG. 4 shows the relationship between the direction angle α and the radial distance r, normalized with respect to the propeller diameter R. As can be seen, as the distance r from the propeller rotation axis A_(P) increases, the direction angle α first of all rises strictly monotonically from α=0.15R, until it passes through a direction angle maximum at the maximum direction angle α_(max). It is advantageous for α_(max) to be >0.2R, in particular for α_(max) to be >0.25R. In the present case, the maximum direction angle is α_(max)=9.3 degrees, and is reached when r=0.3R.

As is shown in FIG. 1, a front propeller hub has a maximum hub radius R₂₀, in which case R₂₀=0.4R.

FIG. 5 shows the thickness distribution. The thickness t is measured at right angles to the chord S (FIG. 3 b).

FIG. 6 shows a view of the propeller pod 14 from above. As can be seen, the traction propeller 22 has a downstream flow angle δ, at which water 36 conveyed by the traction propeller 22 flows away from the traction propeller 22, on a longitudinal plane E_(L) which runs parallel through the traction propeller rotation axis A_(P) and through the shaft 18, in the present case vertically. The direction angle α is chosen such that it differs by at most 10° from the downstream flow angle δ.

The downstream flow angle δ varies with the distance r. This results in the relationship between the direction angle α and the distance r as shown in FIG. 4.

FIG. 6 shows an external contour of a longitudinal pod 38 which, with the shaft 18, is part of the propeller pod 14. FIG. 6 shows a horizontal plane E_(H), which is at right angles to the lateral plane E_(Q) and the longitudinal plane E_(L) and generally runs horizontally when the propeller pod is in the installed position. The direction angles α indicated in FIG. 4 are, however, preferably determined with reference to the direction angle measurement surfaces F_(H) (cf. FIG. 2). The longitudinal axis of the longitudinal pod 38 runs parallel to the propeller rotation axis A_(P). As can be seen, the downstream flow angle δ is measured on the horizontal plane E_(H) and relates to the point at which the traction propeller 22 passes through the longitudinal plane E_(L) adjacent to the shaft 18.

The illustrated propeller pods and pod propulsion systems are particularly suitable for power ranges between 700 kW and 3000 kW. They are also suitable for speeds of more than 40 knots. The varying direction angles make it possible to achieve efficiency improvements of at least 10% over conventional propeller pods.

Suitable propeller diameters are between R=500 mm and R=1500 mm. The maximum direction angle α_(max) is preferably at most 15°. In the present case, symmetrical profiles are used for the cylindrical surfaces shown in the figures.

The proposed system as a pod propulsion system, can be equipped with contrarotating propellers, that is to say propellers which rotate in opposite directions during operation.

LIST OF REFERENCE SYMBOLS

-   10 Marine vessel -   12 Marine vessel hull -   14 Propeller pod -   16 Body -   18 Shaft -   20 Traction propeller shaft -   22 Traction propeller -   24 Pusher propeller shaft -   26 Pusher propeller -   28 Incident-flow edge -   29 Separation edge -   30 Incident-flow point -   32 Separation point -   34 Drive shaft -   36 Water Chord length -   38 Longitudinal pod -   40 Interior -   α Direction angle -   δ Downstream flow angle -   A_(S) Shaft axis -   A_(P) Propeller rotation axis (traction propeller rotation axis)     -   Lateral plane     -   Longitudinal plane -   E_(Q) Direction angle measurement -   E_(L) surface -   F_(H)     -   Distance     -   Traction propeller diameter -   r Hub radius -   R     -   Chord -   R₂₀ Thickness setback     -   Chord length -   S -   D Cross sections -   L -   Q 

1. A propeller pod (14) having (a) a body (16) which (i) has a shaft (18) for attachment to a vehicle (10), in particular to a watercraft, (ii) wherein the shaft (18) extends along a shaft axis (A_(S)) and has at least one cross section (Q) with a chord (S), and (b) at least one propeller shaft (20, 24) for attachment of a propeller (22), (c) wherein the chord (S) runs at a direction angle (α) with respect to a propeller rotation axis (A_(P)) of the propeller shaft (20, 24), wherein (d) the direction angle (α) changes, at least in places, with a distance (r) from the propeller rotation axis (A_(P)).
 2. The propeller pod according to claim 1, comprising a traction propeller shaft (20) for rotation of a traction propeller (22) and a pusher propeller shaft (24) for rotation of a pusher propeller (26), wherein the shaft (18) is arranged between the traction propeller (22) and the pusher propeller (26) with respect to a longitudinal axis of the body (16).
 3. The propeller pod according to claim 2, wherein the traction propeller shaft (20) is designed to rotate the traction propeller (22) in a traction propeller rotation direction (ω₂₂), and the pusher propeller shaft (24) is designed to rotate the pusher propeller (26) in a pusher propeller rotation direction (ω₂₆), which is opposite the traction propeller rotation direction (ω₂₂).
 4. The propeller pod according to claim 1, wherein the direction angle (α) passes through a direction angle maximum as a function of a distance (r) from the traction propeller rotation axis (A_(P)).
 5. The propeller pod according to claim 4, wherein the distance (r) which is associated with the direction angle maximum is at most 0.6 times a propeller radius (R).
 6. The propeller pod according to claim 1, wherein the traction propeller (22) has a downstream flow angle (8), at which water conveyed by the traction propeller (22) flows away from the traction propeller (22), on a longitudinal plane (E_(L)) which runs parallel through the traction propeller rotation axis (A_(P)) and through the shaft (18), and the direction angle (α) differs by at most 10°, in particular by at most 5°, from the downstream flow angle (δ).
 7. The propeller pod according to claim 1, wherein, at least in places, the cross sections (Q) of the shaft (18) are similar in the geometric sense with respect to a cylindrical coordinate system with the origin on the traction propeller rotation axis (A_(P)).
 8. The propeller pod according to claim 1, wherein, at least in places, the cross sections (Q) of the shaft (18) are essentially minor-image symmetrical with respect to a mirror plane on which the chord runs, with respect to the cylindrical coordinate system with the origin on the traction propeller rotation axis (A_(P)).
 9. The propeller pod according to claim 1, wherein, at least in places, the cross sections (Q) of the shaft (18) have a thickness setback (D) of more than 40% and in particular of less than 60%.
 10. The propeller pod according to claim 1, wherein a projection of an incident-flow edge (28) of the shaft (18) onto a lateral plane (E_(Q)) which is at right angles to the traction propeller rotation axis (A_(P)) has a curved profile, at least in places.
 11. The propeller pod according to claim 1, wherein, at least in places, each cross section (Q) has two outermost points (P1, P2) of maximum discrepancy from the chord (S) and a thickness setback point (P_(D)) at which the chord (S) is cut by a connection straight line through the outermost points (P1, P2), wherein the thickness setback points (P_(D)) lie on a curve which is curved at least in places.
 12. The propeller pod according to claim 1, having a drive shaft (34) for driving the traction propeller (22) and/or the pusher propeller (26), wherein, at least in places, the drive shaft (34) runs through an interior (40) of the cross section (Q), wherein the area of the interior (40) is one quarter of the area of the cross section (Q), and has the same centroid.
 13. The propeller pod according to claim 1, wherein a projection of the shaft (18) onto the lateral plane (E_(Q)) is concave or bi-concave.
 14. The propeller pod according to claim 1, wherein the direction angle (α) has a minimum adjacent to the marine vessel hull (12).
 15. A marine vessel (10) having at least one propeller pod (14) according to claim
 1. 16. The marine vessel (10) according to claim 15, having two and only two propeller pods (14) according to claim
 1. 17. The marine vessel (10) according to claim 15, wherein the marine vessel is a yacht. 